Treatment of reformed hydrocarbons with a zinc oxide-zinc chromite catalyst



M. F. FONTAINE ETAL TREATMENT OF REFORMEID HYDROCARBONS WITH A ZINC OXIDE-ZINC CHROMITE CATALYST Filed Aug. 14, 1958 Jan. 3, 1961 United States Patent O TREATMENT F REFORMED HYDROCARBONS WITH A ZINC OXIDE-ZINC CHROMITE CATA- LYST Marc F. Fontaine, Fishkill, and Michael D. Riordan,

Beacon, N.Y., and Jack Ryer, New Brunswick, NJ., assignors to Texaco Inc., a corporation of Delaware Filed Aug. 14, 195s, ser. No. 755,021

12 claims. (Cl. 208.-79)

move the n-pentane which would be isomerized and to f treat the remaining material over a reforming catalyst such as platinum or alumina, chromium oxide on alumina or molybdenum oxide on alumina, extracting the aromatics from the reformate blending them with the isopentane. The straight chain paratns of the reformate would then beh recycled to the catalytic reforming operation. However, this treatment, although it may result in a certain amount of improvement in the octane number is not too satisfactory for the production of the currently required high octane motor fuels as to meet this demand the catalytic reforming must be conducted under extremely severe conditions to the detriment of the catalyst.

In the refining of naphthas to produce high octane motor fuels, the presence of the Cs-Ca normal parains presents a problem. These Cs-Ca normal parafns have particularly low octane numbers. For example, n-hex ane has an octane number of 24.8, n-heptane has an octane number of 0, and n-octane has an octane number of -l7. Obviously the presence of the C-C normal parains is undesirable in a high octane motor fuel since their presence requires additional amounts of high octane components to obtain the desired octane level. However, conversion of these paraflins to high octane components presents a problem. Ordinary isomerization methods, although they do increase the octane number of the aforementioned normal parains do not increase the octane numbers sutiiciently to justify their commercial usage. For example, 2-methylpentane or isohexane has an octane number of 73, Z-methylhexane or isoheptane has an octane number of 45 and Z-methylheptane has an octane number of 23.8. Other isomers of n-octane such as S-methylheptane and 4-methylheptane have octane numbers of 35.0 and 39.0 respectively.

The C6, C, and C8 normal paraflins are not appreciably affected by catalytic reforming conducted at normal operating conditions. In this type of treatment the main reactions are naphthene dehydrogenation and dehydroisomerization in which cyclohexanes and alkylcyclohexanes are dehydrogenated to benzenes and alkyl tive membered ring naphthenes such as alkylcyclopentanes are isomerized and then dehydrogenated to form aromatics. Consequently, preferred feeds for catalytic reforming operations are high in naphthene content and operating conditions are adjusted for optimum conversion of naphthenes to high octane aromatics. Such conditions are not conducive to the upgrading of C6, C, and, C8 parains and, as a result, this group of hydrocarbons is, to a large extent, unaffected by ordinary catalytic reforming procedures.

Cracking of the Cs-Cs n-parains is economically im- 2,967,143 Patented Jan. 3, 1961 ICC practical. When the C-C bond of any molecule in this range is ruptured, at least one, and in some instances all ofthe crackedrfragmentsare gaseous and therefore unsuitable as motor fuel components.

We have now discovered a process for the production of high octane motor fuel from feed stocks containing C7-C8 and C-Cs normal parafns. In one embodiment of our process, the Ctr-Cs or the Cs-CB fraction is contacted with a zinc oxide-zinc chromite catalyst. In a more specific embodiment of the present invention, a straight run gasoline is fractionated into at least two fractions, one containing C-Ca normal paraffins and boiling from about 100 to about 250 F. and a heavier fraction boiling above about 250 F. The 250 F. -EP fraction is passed in contact with a reforming catalyst. The reformate is treated to separate the aromatics from the normal parains and the normal parallins together with the 100-250 F. fraction is contacted with a zinc oxide-zinc chromite catalyst at elevated temperatures.

One advantage of the present invention is that a multicomponent starting material can be separated into fractions which are upgraded under conditions most suitable for that particular fraction. Another advantage of the present invention is that a fraction containing C-C or C7-C8 normal paratns can be converted to a motor fuel fraction having a greatly improved octane number. Still another advantage is that a straight run naphtha can be converted to a motor fuel of high octane number.

In a more specific embodiment of the invention, a straight run naphtha is separated into a C5 or C5-C6 fraction from which the isopentane is separated from the normal pentane and the latter is subjected to isomerization conditions in the presence of an isomerization catalyst, the Cs-C, or C,-C8 fraction is contacted with a zinc oxide-zinc chromite catalyst and theresidual fraction is contacted with a reforming catalyst, the paratinic components of the reformate being separated from the aromatic components and the' parains then being converted together with the C-C or Cq-Cs fraction in the presence of the zinc oxide-zinc chromite catalyst.

The isomerization of the C5 or C5-C fraction may be etfectcdin the presence of an isomerization catalyst such as aluminum chloride or a noble metal catalyst on an alumina support which may contain combined halogen, at elevated temperatures and pressures. When the catalyst is aluminum chloride, which preferably is promoted with HCl, the temperature may range from about 200 to 300 F. and the pressure from about 200 to 800vp.s.i.g. The conditions employed with a noble metal catalyst such as platinum on silica-alumina catalyst are from 700 to 900 F. and 200-700 p.s.i.g. Residence time is generally from 10-40 minutes. Preferably, hydrogen is added to reduce the formation of coke.

The catalyst used for the treatment of the C-Cs or Cfr-C8 fraction contains two components, namely, zinc oxide and zinc chromite, the zinc oxide being present in amounts ranging from l0 to 90% based on the combined weights of the zinc oxide and zinc chromite. The zinc oxide-zinc chromite catalyst may be used alone or may be deposited on up to or even 95% by weight of a substantially inert base such as silica, alumina, magnesia or mixtures thereof. The catalyst may also be promoted by small amounts of metals or metal oxides or suldes such as cerium, cerium oxide or cerium s'ultide. Catalysts containing 25 to 75% zinc oxide based on the combined weights of the zinc oxide and zinc chromite are preferred. Temperatures of 800-l400 F. may be used although temperatures of 950-ll50 F. are preferred. Space velocities may range from O15-3.0 v./v./hr., a preferred range being 0.5l.5 v./v./hr. Pressures ranging from atmospheric to 1000 p.s.i.g., preferably 250-500 p.s.i.g. may be used.

Ihe catalyst may be prepared according to the following method in which parts are given by weight. A first solution is prepared by dissolving 3.036 parts of C.P.

ammonium dichromate in parts of water and adding 2.4 parts of concentrated ammonium hydroxide in-4 parts of water. A second solution is prepared by dissolving 7.l34 parts of C P. Zn(NO3)2.6H2O 1n 16 parts of water. The trst and second solutions are then mixed by being added slowly and simultaneously at equal rates with good agitation to a vessel containing 4 parts of water. Stirring is continued for 1/2 hour after the addition is complete and then 6 parts of concentrated airimonium hydroxide is added to insure complete precipitation.

The precipitate is filtered and washed three times with 10 parts of water, dried and the dried powder decomposed in small portions by heating to i ncipient decomposition temperature. The decomposition temperature was found to be about 640 F. The decomposed powder is then sieved through mesh, pelleted in 5/2-inch dies with 2% Sterotex (a hydrogenated vegetable fat) and calcined at 750 F. for 12 hours. 2.85 parts of dark brown pellets are obtained.

The resultant catalyst contains 26% zinc oxide and 74% zinc chromite by weight. The composition of the catalyst may be varied using appropriate amounts of ammonium dichromate and zinc nitrate as the starting materials.

For the preparation of a supported catalyst composition containg 80% alumina, 400 parts of the decomposed powder are thoroughly mixed with 1600 parts of alumina which has been dried at 600 F. for two hours. Ten parts of water, 5 parts of Sterotex and one part Alkaterge (an alkylated oxazoline) are added and the mixture pelleted in 5Jg-inch dies. calcined at 1000 F. for three hours.

When the catalyst is intended for use in a uidized system the decomposed powder is ground to a particle size of less than 200 microns in diameter with a major proportion between 20 and 80 microns.

The catalytic reforming may be effected using a catalyst such as platinum on alumina, chromia-alumina or molybdena-alumina. Reforming using the noble metal catalyst is generally conducted at 80G-1000 F., 50 to 750 p.s.i.g., 0.7 to 5 v./v./hr. space velocities with 3-l0 mols of hydrogen recycle per barrel of feed. Ordinarily, the recycle gas will contain at least 80% hydrogen. Preferred reaction conditions for the chromia-alumina catalyst are 950-1000" F., 100-200 p.s.i.g., and space velocities of about 0.7 v./v./hr. When the molybdenaalumina catalyst is used for the reforming, the operation is conducted at temperatures of 8 00 to l000 F. and pressures of 20G-250 p.s.i.g. Hydrogen is recycled at the rate of about 4000-6000 cu. ft./bbl. of feed.

The reformate is then treated to separate the normal parains from the aromatics. This can be effected by several methods. However, the preferred methods are extraction of the aromatics by a solvent having an affinity for aromatics or by the use of a molecular sieve.

`The catalytic reformate containing unreacted straight chain paraffins, isoparafns and aromatics may be subjected to liquid-liquid extraction in which the reformate is passed countercurrently to a selective solvent such as phenol or'aqueous glycol. The aromatics are dissolved in the solvent and the raffinate containing parafns and isoparaiiins is sent to the zinc oxide-zinc chromite reaction zone. The aromatics are then removed from the solvent by distillation.

Another method of separating the aromatics from the n-paraftins is by the use of molecular sieve. Any solid adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons can be employed. lt is preferred, however, to employ as the adsorbent certain natural or synthetic zeolites or alumino-silicates such as a calcium The pellets are then tit) tia)

alumino-silicate which exhibits the property of a molecular sieve, that is, adsorbents made up of porous matter or crystals wherein the pores are of molecular dimension and are of uniform size. A particularly suitable solid adsorbent for the adsorption of straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons is a calcium alumino-silicate manufactured by Linde Air Products Company and designated Type 5A Molecular Sieve. The crystals of this particular calcium alumino-silicate, apparently actually a sodium calcium alumino-silicate, have a pore size or diameter of about 5 Angstrom units, a pore size suicient to admit straight chain hydrocarbons, such as the n-paraftns, to the substantial exclusion of the non-straight chain hydrocarbons, such as the naphthenic, aromatic and the isoparatiins and isoolenic hydrocarbons, e.g. isobutane and higher. This particular selective adsorbent is available in various sizes such as 1/16" and l" in diameter pellets as well as in a finely divided powder form.

Other selective adsorbents may be employed. For example, it is contemplated that selective adsorbents having the property of selectively adsorbing straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons in the manner of a molecular sieve may be obtained by suitable treatment of various oxide gels, especially metal oxide gels of the polyvalent amphoteric metal oxides.

Other suitable selective adsorbents are known and include the synthetic and natural zeolites which, when dehydrated, may be described as crystalline zeolites having a rigid three dimensional anionic network and having interstitial dimensions suiciently large to adsorb straight chain hydrocarbons but suiciently small to exclude the non-straight chain hydrocarbons. The naturally occurring zeolite, chabazite, exhibits such desirable properties., Another suitable naturally occurring zeolite is analcite NaAlSi2O5-H2O which, when dehydrated, and when all or part of the sodium is replaced by an alkaline earth metal, such as calcium, yields a material which may be represented by the formula (Ca, Naz) Al2Si4O122HZO and which, after suitable conditioning, will adsorb straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons. Naturally occurring or synthetically prepared phacolite, gmelinite, harmotome and the like, or suitable modifications of these products by base exchange, may also be used.

The effluent from the reforming or converting operation is treated to separate the normally gaseous materials therefrom. e.g. hydrogen, methane, ethane and propane. At least a portion of the separated and recovered hydrogen is recycled to the reforming or converting operation. The normally liquid components of the efuent are then contacted with the solid selective adsorbcnt material in powdered, beaded, microspheroidal, granular or pelleted form to selectively adsorb the straight chain hydrocarbons therefrom. Although it is preferred to remove substantially all of the straight chain hydrocarbons from the eluent it should be realized that it is not necessary to adsorb or separate all of the straight chain hydrocarbons. The extent or degree of straight chain hydrocarbon removal, especially octane number improvement, in order to produce a high octane gasoline is governed by various factors, economic and otherwise, including capacity of the available equipment, the quality desired in the finished treated product, yield considerations, the composition of the eluent and the like.

The eftluent undergoing treatment for the removal of the straight chain hydrocarbons therefrom may be present either in the liquid phase or in a gas or vapor phase. The capacity of the solid adsorbent material as a selective adsorbent for straight chain hydrocarbons is substantially unaffected by the phase condition of the hydrocarbons in contact therewith, provided, of course. suflicient time is allowed to substantially saturate the adsorbent. It is preferred to maintain the effluent in a vapor phase while in contact with the solid adsorbent. Contacting of the eflluent with the solid adsorbent may be effected by any suitable means for effecting gas-solid or liquid-solid contacting and the selective adsorbent may be maintained in a fixed bed, a moving bed or a uid bed.

When liquid phase contacting is carried'out for the removal of the straight chain hydrocarbons from the eluent, it is preferred to carry out the adsorption opera-v tion at a temperature in the range 50-500 F. or higher, sufhcient pressure being applied, if necessary, to maintain the effluent in the liquid phase. In vapor phase adsorption it is prefererd to carry out the adsorption operation at a temperature at least sufiicient to maintain substantially all of the effluent undergoing treatment in the vapor phase, such as a temperature in the range 30o-700 F. or higher, satisfactory adsorption operations having been carried out at temperatures in the range 35o-650 F.

The eluent undergoing treatment is maintained in contact with the selective adsorbent until substantially all of the straight chain hydrocarbons have been removed therefrom or until the selective adsorbent has become substantially saturated with respect to straight chain hydrocarbons. When the adsorbent is substantially saturated, so that straight chain hydrocarbon adsorption is no longer possible, the petroleum fraction or efuent undergoing treatment is contacted with additional fresh or regenerated adsorbent.

After separating the unadsorbed aromatics from the adsorbent, the straight chain hydrocarbons are desorbed from the adsorbent, thereby regenerating the adsorbent, by contacting the adsorbent with a stripping medium which displaces, purges or sweeps out the adsorbed straight chain hydrocarbons from within the pores of the selective adsorbent. Exemplary of a suitable gaseous stripping medium are nitrogen, methane, hydrogen, flue gas, carbon dioxide, substantially dry natural gas and steam, preferably superheated steam. In general, any normally gaseous inert material is suitable as a stripping medium provided, of course, the molecules thereof are suiciently small to enter the pores of the adsorbent. Super-heated steam is particularly suitable as a stripping medium since not only does it effectively displace the adsorbed straight chain hydrocarbons, but also it can be readily and conveniently separated from the desorbed straight chain hydrocarbons by cooling and condensation. Desirably when super-heated steam is employed as the stripping medium, it is followed by an additional normally gaseous stripping medium, such as an inert purge gas, eg. nitrogen, methane, natural gas, hot air, hydrogen or flue gas, and the like, in order to sweep the steam from within the pores of the adsorbent. The desorption operation may be carried out at any suitable temperature. A description temperature in the range 500-1100 F. has been found to be satisfactory. Although the desorption temperature is usually 100-300 F. higher than the adsorption temperature, such as a temperature in the range 700-1000" F., the desorption operation may be carried out at substantially the same temperature as the adsorption temperature. Desorption of the straight chain hydrocarbons may also be effected n the liquid phase by contacting the adsorbent with a polar liquid, e.g. water, at a suitable elevated temperature, as indicated above.

Reference is now made to the accompanying drawing which illustrates diagrammatically a ow sheet for the practice of the present invention and in connection with which an example of one embodiment of the process of the present invention will be described.

A straight run naphtha boiling up to 410 F. is introducd through line 2l into primary fractionator 22. A fraction boiling up to 100 F. is withdrawn through line 23 and introduced into secondary fractionator 24. Isopentane is withdrawn as overhead from secondary fractionator l24 and sent to blending storage through line 25.

The normal pentane bottoms is introduced with hydrogen from line 44 into isomerization reactor 31 through line 30. Isomerization reactor 31 contains a platinum on alumina isomerization catalyst. Reaction conditions in isomerization reactor 31 are temperature 775 F., pressure 250 p.s.i.g., space velocity 1.0 v./v./hr. and hydrogen rate 2000 s.c.f./bbl. Efuent from isomerization reactor 31 is returned by means of line 32 to secondary fractionator 24 where a separation of isopentane is made from normal pentane. The isopentane withdrawn from secondary fractionator 24 through line 25 has ASTM Research Octane Numbers of 92.3 clear and 105.3 (Weise Scale) containing 3 cc. of TEL/gal. The n-pentane is returned to isomerization reactor 31 through line 30.

A fraction boiling from 100 to about 250 F. and having ASTM Research Octane Numbers of 56.0 clear and 74.0 leaded is withdrawn from primary fractionator 22 and sent to dehydroaromatization zone 40 through line 39 with hydrogen, if so desired from lines 34 and 35. Dehydroaromatization zone 40 contains a catalyst having the following analysis: zinc oxide 5.2 wt. percent, zinc chromite 14.8 wt. percent and alumina wt. percent. Reaction conditions in dehydroaromatization zone 40 may be varied depending on the desired octane number of the product. When the reaction is conducted at atmospheric pressure and a space velocity of 0.2 v./v./hr., the following results are obtained under various temperatures:

Temperature, F 1,000 1,025 1,050 1,075 1,100

ASTM Research Octane N timber:

Clear 66. 1 GS. 8 70. 4 69. 2 71. 2 +3 cc. TEL/gal 79. 4 85. 6 86. 8 8G. 9 87. 5

When the reaction is conducted at a pressure of 500 p.s.i.g., a space velocity of 0.5 v./v./hr., a gas recycle rate of 8000 s.c.f./bbl. and fresh hydrogen input of 1272 s.c.f./bbl. and at varying temperatures, the following re- The etuent from dehydroaromatization zone 40 is sent through line 41 to flash tank 42 where hydrogen is separated from normally gaseous hydrocarbons and when hydrogen is used with the zinc oxide-zinc chromite catalyst is recycled to dehydroaromatization zone 40 through lines 43 and 39. To maintain adequate hydrogen concentration, a portion of this stream, or if no hydrogen is to be recycled all of this stream, may be removed from the system through line 45. The balance of the reaction product is withdrawn from flash tank 42 through line 46 and after stabilization is sent to blending storage.

The residual fraction from primary fractionator 22 is sent to catalytic reformer 51 through line 50, hydrogen being introduced into the stream through lines 34 and 52. Catalytic reformer 51 which contains a platinum on alumina catalyst having a platinum concentration of 0.37 wt. percent is maintained under the following conditions: pressure, 500 p.s.i.g., temperature 975 F. Charge feed rate is maintained at 3.0 v./v./hr., and the recycle gas rate is 8000 s.c.f./bbl. of feed. Eluent from catalytic reformer 51 is sent through line 54 to ash tank 55 where the hydrogen and light hydrocarbon gases are removed and recycled to catalytic reformer 51 through lines 57 and 50. To prevent the build-up of light hydrocarbons in the recycle gas stream, a portion of the overhead from ash tank 55 may be withdrawn from the system through line 58. The normally liquid portion of the effluent from reformer 51 which has a leaded (containing 3 rnl. TEL/gal.) ASTM Research Octane Number of 104.9 (Weise Scale) is then sent to separator 60 through line 59. In separator 60 the normally liquid reformate is contacted in the vapor phase with a selective adsorbent, Linde 5A Molecular Sieve, for the removal of straight chain hydrocarbons therefrom. At a space velocity of about 0.5, a temperature of 460 F. and an absorption time of about thirty minutes the effluent which is substantially free of straight chain hydrocarbons has a leaded ASTM Research Octane Number of 108.1 (Weise Scale). The normal paraffins which were absorbed and which are removed by hydrogen at about 700 F. during the regeneration of the adsorbent are then s'ent to dehydrogenation zone 40 through lines 71, 72 and 39, or alternatively, a portion or all thereof may be withdrawn from the system through lines 71 and 73 for use as jet fuel.

If desired, a portion of the bottoms from secondary fractionator 24 may be sent to dehydroaromatization zone 40 through lines 30, 75 and 39 or to catalytic reformer 51 through lines 30, 75, 77 and 50. It is also possible to send the entire n-parafiin desorbate by means (not shown) to primary fractionator 22 and then subject the n-pentane present to isomerization in reactor 31 and contact thel Cty-C8 fraction with the zinc oxide-zinc chromite catalyst in reactor 40.

In another embodiment, primary fractionator 22 may be operated so that the C-C fraction is removed as overhead and fed to secondary fractionator 24 Ithrough line 23. ln this event secondary fractionator 24 represents a series of fractionators in which the isopentanes and isohexanes are removed through line 25 and normal pentane and normal hexane are sent to isomerization zone 31 through line 30. The feed to dehydroaromatization zone 40 would then be composed principally of Cq-Ca straight chain parafns.

Obviously, many other modifications and variations of the invention may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for the production of a high octane motor fuel which comprises separating a straight run naphtha into a first fraction boiling from about 100 to 250 F. and a second fraction boiling above about 250 F., contacting said rst fraction with a catalyst comprising zinc oxide and zinc chromite and containing between about and 90% zinc oxide based on the combined weights of zinc oxide and zinc chromite at a temperature between about 800 and 1200 F. and a pressure between about 250 and 1000 p.s.i.g. in the presence of added hydrogen in a first reaction zone, passing said second fraction into contact with a reforming catalyst in the presence of hydrogen in a second reaction zone at a temperature between about 800 and 1100 F. and a pressure between about 50 and 750 p.s.i.g., recovering normally' liquid straight chain hydrocarbons from the reaction product of the second reaction zone and introducing at least a portion of said straight chain hydrocarbons together with said first fraction into said first reaction zone.

2. A process for the production of a high octane motor fuel which comprises separating a straight run naphtha into a first fraction boiling below about 250 F. and a second fraction boiling above about 250 F., contacting said first fraction with a catalyst comprising zinc oxide and zinc chromite and containing between about 25 and 75% zinc chromite based on the combined weights of zinc oxide and zinc chromite at a temperature between about 900 and 1100 F. and a pressure between about 250 and 500 p.s.i.g. in the presence of added hydrogen, passing said second fraction into contact with a platinum reforming catalyst in the presence of hydrogen in a second reaction zone at a temperature between about 850 8 and 1000' F. and a pressure between about 50 and 750 p.s.i.g., recovering normally liquid straight chain hydrocarbons from the reaction product of the second reaction zone and introducing at least a portion of said straight chain hydrocarbons together with said first fraction into said first reaction zone.

3. A process for the production of a high octane motor fuel which comprises separating a straight run naphtha in a primary fractionation zone into a first fraction boiling up to about F., a second fraction boiling between about 100 and 250 F. and a third fraction boiling above about 250 F., contacting said first fraction with an isomerization catalyst under isomerization conditions to produce a product having an increased content of isoparains, contacting said second fraction with a catalyst comprising zinc oxide and zinc chromite and containing between 10 and 90% zinc oxide based on the combined weights of zinc oxide and zinc chromite at a temperature between about 800 and 1200 F. and a pressure between about 250 and 1000 p.s.i.g. in the presence of added hydrogen in a second reaction zone, passing said third fraction into contact with a reforming catalyst at a temperature between about 800 and 1100 F. in the presence of hydrogen in a third reaction zone, recovering normally liquid straight chain hydrocarbons from the reaction product of said third reaction zone and introducing at least a portion of said straight chain hydrocarbons together with said second fraction into said second reaction zone.

4. A process for the production of a high octane motor fuel which comprises separating a straight run naphtha in a primary fractionation zone into a first fraction boiling up to about 100 F., a second fraction boiling between about 100 and 250 F., and a third fraction boiling above about 250 F., contacting said first fraction with an isomerization catalyst under isomerization conditions to produce a product having an increased content of isoparaffins, contacting said second fraction with a catalyst comprising zinc oxide and zinc chromite and containing between l0 and 90% zinc oxide based on the combinedweights of zinc oxide and zinc chromite at a temperature between about 800 and 1200 F. and a pressure between about 250 and 1000 p.s.i.g. in the presence of added hydrogen in a second reaction zone, passing said third fraction into contact with a reforming catalyst at a temperature between about 800 and 1100 F. in the presence of hydrogen in a thirdl reaction zone, recovering normally liquid straight chain hydrocarbons from the reaction product of said third reaction zone and introducing at least a portion of said straight chain hydrocarbons into said primary fractionation zone.

5. A process for the production of a high octane motor fuel which comprises separating a straight run naphtha into a first fraction boiling up to about F. a second fraction boiling between about 160 and 250 F., and a third fraction boiling above about 250 F., contacting said first fraction with a platinum isomerization catalyst at a temperature between 700 and 900 F. and a pressure between 200 and 700 p.s.i.g. to produce a product having an increased isoparaffin content, subjecting said product to a fractional distillation to remove a fraction having a high isoparafiin concentration as overhead from said distillation, combining at least a portion of the bottoms from said fractional distillation with said second fraction and contacting the mixture in a second reaction zone with a catalyst comprising zinc oxide and zinc chromite and containing between 10 and 90% zinc oxide based on the combined weights of zinc oxide and zinc chromite at a temperature between about 800 and 1200 F. and a pressure between about 250 and 1000 p.s.i.g. in the presence of added hydrogen, passing said third fraction into contact with a platinum reforming catalyst in the presence of hydrogen in a third reaction zone at a temperature between about 800 and 1100 F., recovering normally liquid straight chain hydrocarbons from the reaction product of said third reaction zone and introducing at least a portion of said straight chain hydrocarbons together with said mixture into the second reaction zone. i

6. A process for the production of a high octane motor fuel which comprises separating a straight run naphtha into a first fraction boiing up to about 100 F., a second fraction boiling between about 100 and 250 F. and a third fraction boiling above about 250 F., contacting said first fraction with an aluminum chloride somerization catalyst at a temperature between 240 and 290 F. and a pressure between 200 and 800 p.s.i.g. to produce a product having an increased isoparaffin content, subjecting said product to a fractional distillation to removea fraction having a high isoparaflin concentration as overhead from said distillation. combining at least a portion of the bottoms from said fractional distillation with said second fraction and contacting the mixture in a second reaction zone with a catalyst comprising zinc oxide and zinc chromite and containing between and 75% zinc 20 oxide based on the combined weights of zinc oxide and zinc chromite at a temperature between about 900 and 1100 F. and a pressure between about 250 and 1000 p.s.i.g. in the presence of added hydrogen, passing said third fraction into contact with a platinum reforming 25 catalyst in the presence of hydrogen in a third reaction zone at a temperature between about 850 and 1000 F., recovering normally liquid straight chain hydrocarbons from the reaction product of said third reaction zone and introducing at least a portion of said straight chain hydrocarbons together with said mixture into the second reaction zone.

7. The process of claim 6 in which the reaction product of the third reaction zone is contacted with a selective adsorbent whereby the straight chain hydrocarbons are separated from the aromatic hydrocarbons, and said aromatic hydrocarbons are combined with said fraction having a high isoparafiin concentration and the reaction product of said second reaction zone.

8. A process for the production of a high octane motor 40 fuel which comprises separating a straight run naphtha into a first fraction boiling from about 100 to 250 F. and a second fraction boiling above about 250 F., contacting said first fraction with a catalyst consisting essentially of zinc oxide and zinc chromite and containing between about l0 and 90% zinc oxide based on the combined weights of zinc oxide and zinc chromite at a ternperature between about 1025 and 1100 F. and a pressure between about 250 and 1000 p.s.i.g. in the presence of added hydrogen in a tirst reaction zone, passing said second fraction into contact with a reforming catalyst in the presence of hydrogen in a second reaction zone at a temperature between about 800 and 1100 F. and a pressure between about and 750 p.s.i.g., recovering normally liquid straight chain hydrocarbons from the reaction product of the second reaction zone and introducing at least a portion of said straight chain hydrocarbons together with said first fraction -into said irst reaction zone.

9. The process of claim 8, in which the zinc oxidezinc chromite catalyst is supported on alumina.

10. A process for the production of a Ahigh octane motor fuel which comprises separating a straight run naphtha into a first fraction boiling from about F. to 250 F. and a second fraction boiling above about 250 F., contacting said first fraction with a catalyst comprising zinc oxide and zinc chromite and containing between about 10% and 90% zinc oxide based on the combined weights of zinc oxide and zinc chromite at a temperature between about 800 and 1200 F. and a pressure between about 250 and 1000 p.s.i.g. in the presence of added hydrogen in a first reaction zone, passing said second fraction into contact with a reforming catalyst in the presence of hydrogen in a second reaction zone at a temperature between about 800 and 1100 F. and a pressure between about 50 and 750 p.s.i.g., separating the reaction product of said second reaction zone into an aromatic rich fraction and a fraction rich in normally liquid straight chain hydrocarbons and introducing at least a portion of said fraction rich in normally liquid straight chain hydrocarbons together with said first fraction into said first reaction zone.

11. The process of claim `l0 in which the reaction product from the second reaction zone is contacted with a selective solvent having an afiinity for aromatic hydrocarbons.

l2. The process of claim 11 in which the reaction product from the second reaction zone is'passed in contact with a selective adsorbent to effect separation of the reaction product into an aromatic rich fraction and a fraction rich in normally liquid straight chain hydrocarbons.

References Cited in the file of this patent UNITED STATES PATENTS Christensen et a1. Dec. 31, 1957 

1. A PROCESS FOR THE PRODUCTION OF A HIGH OCTANE MOTOR FUEL WHICH COMPRISES SEPARATING A STRAIGHT RUN NAPHTHA INTO A FIRST FRACTION BOILING FROM ABOUT 100 TO 250*F. AND A SECOND FRACTION BOILING ABOVE ABOUT 250*F., CONTACTING SAID FIRST FRACTION WITH A CATALYST COMPRISING ZINC OXIDE AND ZINC CHROMITE AND CONTAINING BETWEEN ABOUT 10 AND 90% ZINC OXIDE VASED ON THE COMBINED WEIGHTS OF ZINC OXIDE AND ZINC CHROMITE AT A TEMPERATURE BETWEEN ABOUT 800 AND 1200*F. AND A PRESSURE BETWEEN ABOUT 250 AND 1000 P.S.I.G. IN THE PRESENCE OF ADDED HYDROGEN IN A FIRST EACTION ZONE, PASSING SAID SECOND FRACTION INTO CONTACT WITH A REFORMING CATALYST IN THE PRESENCE OF HYDROGEN IN A SECOND REACTION ZONE AT A TEMPERATURE BETWEEN ABOUT 800 AND 1100*F. AND A PRESSURE BETWEEN ABOUT 50 AND 750 P.S.I.G., RECOVERING NORMALLY LIQUID STRAIGHT CHAIN HYDROCARBONS FROM THE REACTION PRODUCT OF THE SECOND REACTION ZONE AND INTRODUCING AT LEAST A PORTION OF SAID STRAIGHT CHAIN HYDROCARBONS TOGETHER WITH SAID FIRST FRACTION INTO SAID FIRST REACTION ZONE. 